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| <head> |
| <title>monitor-enter</title> |
| <link rel=stylesheet href="opcode.css"> |
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| <body> |
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| <h1>monitor-enter</h1> |
| |
| <h2>Purpose</h2> |
| |
| <p> |
| Acquire the monitor for the indicated object. |
| </p> |
| |
| <h2>Details</h2> |
| |
| <table class="instruc"> |
| <thead> |
| <tr> |
| <th>Op & Format</th> |
| <th>Mnemonic / Syntax</th> |
| <th>Arguments</th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr> |
| <td>1d 11x</td> |
| <td>monitor-enter vAA</td> |
| <td><code>A:</code> reference-bearing register (8 bits)</td> |
| </tr> |
| </tbody> |
| </table> |
| |
| <h2>Constraints</h2> |
| |
| <ul> |
| <li> |
| A must be a valid register index for the current stack frame. |
| </li> |
| <li> |
| Register vA must contain a reference to an object. |
| </li> |
| </ul> |
| |
| <h2>Behavior</h2> |
| |
| <ul> |
| <li> |
| An attempt is made for the current thread to acquire the monitor of the |
| indicated object. Various results are possible: |
| <ul> |
| <li> |
| If the monitor is not owned by any thread at this point, then the |
| current thread becomes owner of the monitor. The entry count of the |
| indicated object is set to 1. |
| </li> |
| <li> |
| Otherwise, if the monitor is owned by the same thread that attempts the |
| acquiration, then the entry count of the indicated object is increased |
| by 1. |
| </li> |
| <li> |
| Otherwise the monitor is owned by a different thread. The current thread |
| sleeps until the monitor of the object is released. Once that happens, a |
| new attempt to acquire the monitor is made, as described here. There is |
| no guarantee that the second attempt (or any subsequent attempt) will be |
| successful. |
| </li> |
| </ul> |
| </li> |
| </ul> |
| |
| <h2>Exceptions</h2> |
| |
| <ul> |
| <li> |
| NullPointerException if vA is null. |
| </li> |
| <li> |
| IllegalMonitorStateException if the entry count exceeds an |
| (implementation-dependent) upper bound for recursive monitor entries. Note |
| that it is unlikely this bound is ever hit, since for most implementations |
| the call stack will overflow before. |
| </li> |
| </ul> |
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